This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Coccolithophores are marine unicellular algae, notable for the intricate calcite (CaCO3) structures (coccoliths)which surround each cell. They can form vast oceanic blooms, representing the largest class of calcifying organisms on the planet and constituting a fundamental part of the global carbon cycle in a number of ways. X-ray tomography provides a unique way to investigate the factors described above. We plan to grow E. huxleyi at CO2 concentrations of 300 and 750 ppm.The outer coccoliths will be dissolved by brief exposure to mild acid (pH 5.2), and the cells frozen. We will scan at the appropriate energies to image calcium (L-edge energy 400 eV), magnesium and carbon (K-edge energies of 1.31 and 0.28 keV respectively).